The present invention relates to a method and apparatus for controlling a rotary vacuum packaging machine that rotates, along an endless track, a large number of pressure-proof chambers each for forming a vacuum space inside, and a bag-forming and -filling packaging machine for feeding an unsealed wrapped article into each pressure-proof chamber of the vacuum packaging machine so that the rotary vacuum packaging machine and the bag-forming and -filling packaging machine operate in synchronism.
As disclosed in U.S. Pat. No. 5,347,791, a bag-forming and -filling packaging machine called an xe2x80x9cautowrapperxe2x80x9d is structured so that band-shaped films rolled around a support shaft are drawn out through a bag former by rotation power of a first motor so as to be formed into a tube. Then, a large number of packaged articles are loaded in the tube film in tandem at regular intervals by means of a conveyor rotated by power of a second motor. Subsequently, the tube film is sequentially seal-cut at a position between each two packaged articles by means of a seal bar rotated by power of a third motor, and are then unloaded as packaged articles. These servo motors are controlled by a controller, that is, an automatic calculation device so that the rotation angles of the first and third motors are controlled based on the rotation angle of the second motor. That is, the bag-forming and -filling packaging machine is structured to simultaneously operate the transfer speed of band-shaped films, a pitch with which the conveyor loads packaged-articles, and the rotation cycle of the seal bar, mutually.
On the other hand, JP-A-8-16941, which has been laid-open in Japan, discloses a rotary vacuum packaging apparatus for transferring unsealed packaged articles sequentially unloaded from a bag-forming and -filling packaging machine, onto surface plates moved along an endless track at regular intervals, subsequently placing a cover member on each of the surface plate, and then vacuum-packaging the packaged article in a pressure-proof chamber formed of the surface plate and the cover member. Operation of each motor of this apparatus is controlled so that reference pulses from a main motor for driving a rotor of the vacuum packaging apparatus synchronize a seal bar power motor with the main motor. Further, pulse signals from the power motor for the seal bar synchronize rotation of a motor for transferring the band-shaped films with rotation of a motor for transferring the packaged articles.
Thus, if loads on the vacuum packaging machine vary to cause a correction signal to be transmitted from a controller to the bag-forming and -filling packaging machine, the rotations of the three motors are corrected step-wise, thereby necessarily resulting in a rapid motor correction operation, which leads to frequent failures.
Thus, it is an object of the present invention to eliminate the master-server relationship among the motors of the bag-forming and -filling packaging machine to allow correction operation for each motor to be slowly performed depending on variations in loads on the vacuum packaging machine, thereby reducing the frequency of failures in the motors.
To attain this object, the present invention is comprised of a rotary vacuum packaging chamber for using a main motor to transport, along an endless track, a large number of pressure-proof chambers arranged at regular intervals, while vacuum-sealing an unsealed packaged article inside each of the pressure-proof chambers being transported, and a pulse generator for converting the rotation angle of the main motor into a pulse signal and inputting it to a main controller, wherein the transportation pitch of the pressure-proof chambers is determined from pulses input to the main controller and wherein in accordance with modulation of the pitch of the pulses, servo motors for operating the bag-forming and -filling packaging machine are simultaneously corrected while uncoupled from one another so that the rotation angles of the individual servo motors agree with the pitch of each pressure-proof chamber.
The main controller obtains pulses generated by a pulse transmitter in order to determine the transportation pitch of the pressure-proof chambers, and synchronizes operation of each servo motor with operation of the main motor so that the transportation pitch of the pressure-proof chambers agrees with each of a film transfer pitch, a packaged-article loading pitch, a sealer driving cycle, and a packaged article unloading pitch in the bag-forming and -filling packaging machine. That is, the rotation of each servo motor is allowed to follow the rotation of the main motor. If a variation in loads on the main motor varies the pulse pitch, the main controller individually transmits an arithmetic-operation signal through each control element to a corresponding one of the servo motors connected to the main controller, so that the rotation of each servo motor is simultaneously controlled by the correction effect of each control element. In summary, since the plurality of servo motors are controlled to follow variations in the motion of the main motor, the speed of each servo motor varies with variations in the motion of the main motor caused by variations in loads thereon. Compared to the conventional control shown in xe2x80x9cBackground of the Inventionxe2x80x9d as correcting motion step-wise, the present configuration requires only one-step operation, thereby improving the failure rate.